A flip-chip structure in which electronic components such as ICs are bonded to a printed pattern on a substrate via solder balls or gold (Au) balls has attracted attention because it is free of a wire for obtaining electric conductivity unlike a face-up structure and is able to load a small-size electronic component by a relatively simple process (for example, refer to Patent Document 1). Therefore, the structure has been considered for possible applications to a light-emitting diode lamp equipped with semiconductor light-emitting devices.
FIG. 11A is a bottom view showing a conventional flip-chip type semiconductor light-emitting device, and FIG. 11B is a sectional pattern diagram corresponding to the line k-k′ given in FIG. 11A. As shown in FIG. 11B, a conventional flip-chip type semiconductor light-emitting device 101 (hereinafter referred to as light-emitting device 101) is substantially constituted of a sapphire substrate 102, a semiconductor layer 103 stacked on the substrate 102, a positive electrode 104 provided on the semiconductor layer 103 and a negative electrode 105 provided at a site where the semiconductor layer 103 is partially removed by etching.
The semiconductor layer 103 formed on the substrate 102 is constituted by sequentially laminating a buffer layer 103a composed of aluminum nitride, an n-GaN layer 103b, a lower cladding layer 103c composed of n-GaN, an active layer (light-emitting layer) 103d which is to act as a well layer of a single quantum well structure, an upper cladding layer 103e composed of p-AlGaN, and a contact layer 103f composed of p-GaN. A recess 103g for fixing the negative electrode is formed at a part of the semiconductor layer 103 by removing the lower cladding layer 103c, the active layer (light-emitting layer) 103d, the upper cladding layer 103e and the contact layer 103f until exposure of the n-GaN layer 103b. 
The positive electrode 104 is constituted of a first electrode layer 104a in which Pt film (thickness of 2 nm), ANC film (thickness of 60 nm) and Rh film (thickness of 30 nm) are stacked sequentially, a second electrode layer 104b in which Pt film (thickness of 2 nm) and Rh film (thickness of 120 nm) are stacked sequentially and a third electrode layer 104c in which Cr film (thickness of 40 nm), Ti film (thickness of 100 nm) and Au film (thickness of 200 nm) are stacked sequentially. Then, an ohmic junction is formed between the first electrode layer 104a and the semiconductor layer 103 (contact layer 103f).
Furthermore, the negative electrode 105 is constituted of an electrode layer 105a in which the Cr film (thickness of 40 nm), Ti film (thickness of 100 nm) and Au film (thickness of 200 nm) are stacked sequentially. The negative electrode 105 is, as described above, arranged on the recess 103g for fixing the negative electrode. Then, an ohmic junction is formed between the electrode layer 105a and the semiconductor layer 103 (n-GaN layer 103b).
Then, the conventional light-emitting device 101 is designed to radiate light mainly from the active layer (light-emitting layer) 103d to the substrate 102 side. As shown in FIG. 11A, the positive electrode 104 is formed substantially all over the semiconductor layer 103. This is because light from the light-emitting layer 103d is effectively reflected by the positive electrode 104 to radiate the light to the substrate 102 side and also electric current is allowed to flow effectively to p-type semiconductor layers (upper cladding layer 103e and contact layer 103f) which are relatively low in electric conductivity.
On the other hand, as shown in FIG. 11A, the electrode area of the negative electrode 105 is approximately one tenth that of the positive electrode 104. This is because the negative electrode 105 is bonded to an n-type semiconductor layer (n-GaN layer 103b) which has relatively high electric conductivity, thereby making it possible for electric current to flow effectively despite a small forming region of the negative electrode 105.
This light-emitting device 101 is fixed to a printed circuit board, and the substrate 102 side is placed upward, and used as a light-emitting diode lamp. FIG. 12 is a plan pattern diagram showing a printed circuit board which is used to mount a light-emitting diode lamp. The printed circuit board 110 illustrated in FIG. 12 is substantially constituted of an aluminum substrate 110a, an insulating layer 110b composed of a resin layer stacked on the aluminum substrate 110a, an electrode 111 for the positive electrode composed of Cu foil formed on the insulating layer 110b and an electrode 112 for the negative electrode. The electrodes 111 and 112 respectively for the positive electrode and the negative electrode are shaped so as to correspond respectively to the positive electrode 104 and the negative electrode 105 of the light-emitting device 101 when viewed from above.
Furthermore, printed patterns 111a and 112b are provided on the electrodes 111 and 112, respectively.
FIG. 13 illustrates a light-emitting diode lamp 120 wherein a light-emitting device 101 is packaged on a printed circuit board 110. As shown in FIG. 13, the light-emitting device 101 is arranged in such a manner that the positive electrode 104 and the negative electrode 105 face the printed circuit board 110. A soldering film 121 composed of AuSn for bonding is interposed between the positive electrode 104 and the electrode 111 of the printed circuit board 110. Furthermore, a soldering film 122 composed of AuSn for bonding is also interposed between the negative electrode 105 and the electrode 112. As described above, the light-emitting device 101 is soldered to the printed circuit board 110, thereby providing a flip-chip structure. In the light-emitting diode lamp 120 illustrated in FIG. 13, since an aluminum substrate 110a constituting the printed circuit board 110 is excellent in heat dissipation, heat generated in association with motions of the light-emitting device 101 can be effectively released via the printed circuit board 110.
In assembling the light-emitting diode lamp 120, first, AuSu alloy particle-containing soldering paste is coated respectively on the positive electrode 104 and the negative electrode 105 of the light-emitting device 101 in such a manner that the electrodes 104 and 105 are superimposed respectively on the electrodes 111 and 112 of the printed circuit board 110, and arranged and fixed temporarily. Then, the light-emitting device 101 and the printed circuit board 110 are charged into a furnace to effect re-flow, and AuSn alloy particles are melted and then solidified, by which soldering films 121 and 122 are formed to bond the electrodes 104 and 105 with the electrodes 111 and 112 of the printed circuit board 110, respectively. Thereby, the light-emitting diode lamp 120 is manufactured.
Patent Document 1 Japanese Published Unexamined Patent Application No. 3-255640.